We request support to perform data analyses in the NAS-NRC Twin Registry using state-of-the-art statistical methodologies. The registry is the largest existing in the United States and is the only registry for which longitudinal data are available. This resource is currently underutilized, and only a limited number of publications have addressed issues relevant to cardiovascular epidemiology. Given recent advances in statistical methods for twin data, this resource represents a unique opportunity to address timely issues pertinent to the role of genetic and environmental factors in the manifestation of cardiovascular disease and related risk factors. The planned analyses will expand, confirm, and cross-validate related findings in the NHLBI Twin Study, which is only a small subset of the registry. Specific objectives of this proposal are: (1) To determine the extent to which an increased familial risk in CVD mortality among twins is mediated by similarities in behavioral risk factors such as smoking, food habits, changes in weight since induction, physical activity, and socioeconomic variables. (2) To assess the contribution of genetic and environmental factors to twin similarities in health behaviors. (3) To investigate the genetic determinants in the continuity or discontinuity of health behaviors in adult life (e.g., smoking cessation, weight gain). We expect at least four publications to result from these analyses.